Any conventional amplifiers used for transmission cables and so on in CATV are high-power branch amplifiers using LCs therein and plural amplifiers for special purposes are used in combination for each band.
Such a conventional amplifier is, however, required to be of a negative feedback type to eliminate distortions, which may cause oscillation and so on in a GHz-band thereby rendering the amplifiers unstable as well as rendering the circuit configuration complicated.
The present invention has been achieved in perception of the facts that if the output current of a transistor is reduced, for example, to about 10 mA, a possible distortion in the output of the transistor shall be reduced greatly, while the upper limit of operational frequency f.sub.T shall be raised to about 3 GHz, and that the distortion in the output current of the transistor can be canceled by inserting into its input circuit a transistor being the same characteristic as the former transistor. It is an object of the present invention to provide a high-quality wide-band amplifier which eliminates the above drawbacks due to use transistors.